The present invention relates generally to brake units and more particularly to brake units of the oil shear type having internal oil pump means operative to selectively circulate oil in response to rotation of the brake unit in a preselected direction.
Various types of brake units are used in conjunction with well drilling rigs such as those used in construction of oil and gas wells. In one manner of drilling oil and gas wells, a length or stand of pipe is connected to a drill bit which is then rotated thereby drilling deeper into the ground. As the well progresses, it is necessary to install a casing which usually consists of stands of larger diameter pipe connected together which operate to guide the drilling apparatus, support surrounding ground formations, seal the sides of the opening as well as other various purposes. The drilling apparatus generally comprises a drawworks assembly which includes a cable drum, driving apparatus for rotatably driving the cable drum, a main brake and a secondary brake often referred to as a mode absorber. The drawworks performs various functions including raising and lowering the drilling pipe and bit for bit replacement, and connection of additional stands of drill pipe as well as to control drilling pressure. Also, the drawworks may be used to assist in installation of the casing as well as replacement thereof should the casing become worn due to extended drilling operations. The main brake is commonly intimately associated with the cable drum of the drawworks operating to stop and hold the drilling apparatus, pipe stands or the like at any desired position whereas the mode absorber operates in the nature of a governor to limit lowering speeds. The mode absorber may be in the form of a water brake which utilizes the resistance of a turbine rotating through a fluid for example. While the mode absorber does reduce the rate of acceleration thereby increasing the available response time for an operator to effect corrective measures, it will constitute a significant drag during raising operations unless disconnected from the drawworks. If the mode absorber is allowed to remain connected to the drawworks, power consumption may be significantly increased as well as operating speeds reduced due to this drag. Thus, it is generally necessary to disconnect the mode absorber during raising. Not only does the disconnecting procedure require loss of valuable operating time but also the disconnection of the mode absorber eliminates the added safety factor due to the increased response time provided thereby within which the operator may actuate the brake should a power failure be encountered. Further, such absorbers constitute an additional piece of equipment requiring maintenance as well as additional controls to adjust the resistance for varying lowering speeds.
Accordingly, the present invention provides a brake unit for use in conjunction with such drawworks which combines in a single unit apparatus capable of performing the functions heretofore performed by both the main brake and mode absorber and further which is substantially more economical and efficient to operate as well as providing for fail-safe operation to protect associated drilling equipment from damage due to a power failure, brake through of the drilling bit into an underground cavern or any other such occurrences.
The present invention includes an input shaft operatively connected to the drawworks which drives an internal oil gear pump which is operative to circulate a large volume of oil through the brake unit along a first flowpath in response to rotation of the input shaft in one direction such as during lowering of pipe stands so as to cool and lubricate the brake discs and plates. During a raising operation, the gear pump operates to circulate oil through an alternative low resistance flowpath so as to reduce the drag due to pump operation. Thus, during lowering of pipe or other tooling or equipment into the well, the gravitational forces acting thereon also operate to drive this internal oil pump thereby circulating large quantities of oil through the brake unit. As this lowering operation represents the severest duty for the brake unit, the need for oil circulation for both cooling and lubricating is greatest during this mode of operation. However, during raising of pipe or equipment from the well, it is desirable to reduce drag on the driving equipment to an absolute minimum so as to allow such operations to be completed as rapidly as possible and with a minimum consumption of power. Heretofore, it has often been desirable to expend additional time and labor to disconnect the brake unit from the drawworks in order to reduce this drag. In the present invention, the oil flowpath within the brake unit is designed to minimize the drag resulting therefrom during such raising operations thereby eliminating the time consuming job of disconnecting the brake unit from the drawworks. This also enables the brake unit to act as a safety back-up during raising operations. Should an equipment failure be encountered during a raising operation, the internal oil pump will immediately be actuated in response to the descending tooling and will operate to override the control fluid pressure to actuate the brake unit thereby minimizing the possibility of equipment damage resulting therefrom.
Additional advantages and features of the present invention will become apparent from the following description of a preferred embodiment taken in conjunction with the drawings and claims appended hereto.